The invention relates to a process for producing ethylene oxide and an integrated system for producing ethylene oxide.
In recent years increasing attention is given to the exploration and utilisation of natural gas resources around the globe. A disadvantage of natural gas with respect to oil is the difficulty to transport large volumes of natural gas from the source to the market. One way of efficiently transporting natural gas is by liquefying the natural gas and to transport the liquefied natural gas (LNG). Another way is to convert the methane in the natural gas to liquid hydrocarbons using a Gas-to-Liquid process (GtL). The GtL products are typically liquid and can be transported in a similar way as traditional oil and oil products.
Besides methane, the natural gas typically comprises other hydrocarbons such as ethane, propane, and butanes. Such a natural gas is referred to as wet gas. The latter two can be added to the LPG pool, however, ethane cannot. Moreover, for various reasons the ethane content in the natural gas supplied to an LNG or GtL process is restricted and therefore a significant part of the ethane must be removed from the natural gas prior to providing the natural gas to either a LNG or GtL process.
Although, the application of ethane is limited, typically ethane is combusted in a furnace to provide heat; its corresponding olefin ethylene is a base chemical with a wide application and is of great commercial interest. Ethane can be converted into ethylene, e.g. using a thermal cracking process. Subsequently, the ethylene can be used to produce e.g. polyethylene, styrene or mono-ethylene-glycol. The conversion of ethane to ethylene is highly endothermic and requires significant energy input. In addition, the capex for the ethane to ethylene process, in particular the back-end work-up section, and the subsequent ethylene conversion processes is high and a minimum ethylene production capacity is required to make it economically benign.
When, the ethane content in the natural gas is too low, and consequently insufficient ethane is available, the ethane/ethylene route become unattractive.
This problem becomes even more pronounced, in case the natural gas is withdrawn from relatively small reservoirs, especially those located in remote, isolated locations, also referred to as stranded natural gas. Of course, this stranded natural gas may be converted to LNG or GtL products. However, this requires the stranded gas reservoir to sustain a minimum production level per day in order to make the investments worthwhile. Typically, such stranded natural gas reservoirs cannot achieve sufficient production levels to sustain a GtL or LNG plant. In addition, insufficient ethane is co-produced to sustain an ethane to ethylene process and subsequent ethylene conversion processes.
It has been suggested to combine an ethane steam cracker with an Oxygenate-to-Olefin (OTO) process, which can produce additional ethylene. For instance, C. Eng et al. (C. Eng, E. Arnold, E Vora, T. Fuglerud, S. Kvisle, H. Nilsen, Integration of the UOP/HYDRO MTO Process into Ethylene plants, 10th Ethylene Producers' Conference, New Orleans, USA, 1998) have suggested to combine UOP's Methanol-to-Olefins (MTO) process with a naphtha or ethane fed steam cracker. It is mentioned that by combining both processes sufficient ethylene can be produced, while coproducing valuable propylene. A disadvantage mentioned by C. Eng et al. is the fluctuating price of methanol, which is the primary feed to the MTO reaction.
In WO 2009/039948 A2, a combined stream cracking and OTO process is suggested for preparing ethylene and propylene. According to WO 2009/039948 A2, in this process, a particular advantage is obtained by combing the back-end of both processes. The methanol feedstock is produced from methane, requiring a sufficient supply of methane.
In US2005/0038304, an integrated system for producing ethylene and propylene from an OTO system and a steam cracking system is disclosed. According to US2005/0038304, in this process, a particular advantage is obtained by combining the back-end of both processes. The methanol feedstock to the OTO process is produced from synthesis gas. However, according to US2005/0038304 the production of methanol from synthesis gas has high energy requirements due to the endothermic nature of the synthesis gas production process. Such an endothermic synthesis gas production process is normally steam methane reforming.
As mentioned herein above, ethylene is a suitable intermediate to produce mono-ethylene-glycol. Monoethylene-glycol is a liquid at room temperature and can therefore be suitably transported. Mono-ethylene-glycol is produced by first oxidising ethylene to ethylene oxide. The disadvantage of converting the ethylene to mono-ethylene-glycol is that carbon dioxide is produced as a by-product of the ethylene oxidation process. This carbon dioxide has no further purpose and therefore must be sequestered or otherwise captured and stored in order reduce the carbon dioxide penalty of the process.
There is a need in the art for a process for preparing ethylene oxide and optionally mono-ethylene-glycol by an integrated ethane cracking and OTO process with a reduced carbon dioxide production.